Background scanning is used by several network selection algorithms to enable a mobile station to periodically search for another network. The search can be guided by a number of different criteria set by the network operator and/or by the user. As an example, if a user employs network operator #1 to obtain their service, and if the mobile station is powered up in an area where only network operator #2 is available, the mobile station will register with and camp on a channel of network operator #2. However, the mobile station may periodically leave the channel to network operator #2 to search or scan for a channel provided by network operator #1. This type of operation is typically performed as a background task, and hence can be referred to as background scanning.
Background scanning is very different than cell reselection operations. In cell reselection the mobile station typically scans neighbor cells belonging to the currently selected network operator to locate a cell to which it may immediately, or in the future, hand-off to. A list of neighbor cells to be scanned can be provided by the network and transmitted to the mobile station, and the mobile station may report the results of the neighbor cell scanning operation back to the network.
Background scanning, in contradistinction, provides a mechanism for a primary network operator of the mobile station to force the mobile station to a higher priority network when it is camped on a lower priority network.
Background scanning also involves the mobile station temporarily losing service on the currently registered channel, without the knowledge of the network operator, so that the mobile station can re-tune its receiver to scan for another network operator.
There are two primary problems with background scanning as it is currently performed. The first problem results from the mobile station leaving the registered channel to evaluate other channels in its search for a better network. During the period of time that the mobile station is evaluating other channels, it will miss any messages sent by the base station to which the mobile station is registered sends. This means that the mobile station will miss, by example, pages, short message service (SMS) messages and authentication during background scanning. The second problem results from the periodicity of the background scanning. Since the mobile station will periodically search for better networks while it would normally be camped with its transmitter, digital signal processor (DSP) and central processor unit (CPU) powered down in a sleep mode, the background scanning results in a reduction in battery life. Therefore, it is desirable to reduce the number of background scans that the mobile station perform without locating a better network. This problem is further aggravated by the fact that in some areas there is no better network available. As such, the power consuming background scanning operations will fail to find better service.
If the severity of this problem is reduced by simply increasing the time between background scans, the mobile station is required to reside on a low priority network for a longer period of time. A problem with this situation is that it is possible for the mobile station to camp on a network that does not allow it to receive calls, or that does not allow the mobile station access to desired services.
Thus, in these situations it is imperative that the background scans occur frequently in order to reduce the period without service.
Currently, the decision to enable background scanning is made in the mobile station based upon network identification parameters. Therefore, for time division, multiple access (TDMA) networks, the decision to perform a background scan is based on the System Identifier Code (SID) and the System Operator Code (SOC). These parameters can provide the mobile station with enough information to determine which market (network operator) the mobile station is currently camped on. For example, the mobile station can determine that it is currently located in some metropolitan area. Therefore, if a situation exits where, within the overall metropolitan area, there is one small area (perhaps a border with another market area) that has a higher priority network, the background scanning will be performed within the entire metropolitan area.
The decision to enable background scanning for GSM-type networks is based on the Public Land Mobile Network (PLMN), which gives the identification of the operator and the country. This means that, if a situation exists where, within the United States, there is one small area (perhaps a border with another market area) that has a higher priority, background scanning will be performed in the entire United States. In many cases, forcing background scanning on such a broad scale will result in a very high percentage of unproductive background scans.
Another problem that exists in current system selection approaches relates to finding and selecting non-public systems, such as private and residential systems. The only technique to perform this task now is to recognize the public channels that are used in the vicinity of the non-public system. These channels are stored from the neighbor list of the non-public system and, as a result, the non-public system can only be found when the mobile station 100 is camped in the same license block (in the same set or block of frequencies) as the non-public system. Furthermore, if channel allocation changes around the non-public system, the mobile station will not be able to locate the non-public system automatically.
It can thus be appreciated that there is a need to improve the efficiency of mobile station system selection operations.